Wireless terminal with dual band antenna arrangement and RF module for use with dual band antenna arrangement

ABSTRACT

A wireless terminal having a dual band antenna arrangement which comprises a planar inverted-F antenna ( 10 ) having a first ( 12 ) for signals in a first, lower frequency band, for example the GSM band, a second feed ( 14 ) for signals in a second, higher frequency band, for example the DCS band, and a ground pin ( 16 ). A first coupling stage ( 26 A) couples the transmit and receive paths of a first transceiver (GSM) to the first feed and a second coupling stage ( 26 B) couples the transmit and receive paths of a second transceiver (DCS) to the second feed. Each of the first and second coupling stages comprise a quarter wavelength transmission line ( 50 A,  50 B) having a first end coupled to the respective transmit signal path and a second end coupled by band pass filter ( 52 A,  52 B) to the respective receive signal path. A first PIN diode (D 1 , D 3 ) couples a transmit signal path to the first end of the respective quarter wavelength transmission line and to the respective feed ( 12, 14 ) and a second PIN diode (D 2 , D 4 ) second end of the respective quarter wavelength transmission line to ground. In operation when transmitting in one of the bands, the first and second PIN diodes of the relevant coupling stage are switched-on, whilst the PIN diodes in the other coupling stage are off and when in a receiving mode all the PIN diodes are off. The signal being received by one of the transceivers is reflected by the band pass filter in the coupling stage of the other transceiver.

TECHNICAL FIELD

The present invention relates to wireless terminal, for example acellular telephone, having a dual-band antenna arrangement comprising asubstantially planar patch antenna, and to a module incorporating suchan arrangement. In the present specification, the term dual-band antennarelates to an antenna which functions satisfactorily in two (or more)separate frequency bands but not in the unused spectrum between thebands.

BACKGROUND ART

Wireless terminals, such as mobile phone handsets, typically incorporateeither an external antenna, such as a normal mode helix or meander lineantenna, or an internal antenna, such as a Planar Inverted-F Antenna(PIFA) or similar.

Such antennas are small (relative to a wavelength) and therefore, owingto the fundamental limits of small antennas, narrowband. However,cellular radio communication systems typically have a fractionalbandwidth of 10% or more. To achieve such a bandwidth from a PIFA forexample requires a considerable volume, there being a directrelationship between the bandwidth of a patch antenna and its volume,but such a volume is not readily available with the current trendstowards small handsets. Further, PIFAs become reactive at resonance asthe patch height is increased, which is necessary to improve bandwidth.

U.S. Pat. No. 6,061,024 discloses a duplexing antenna for a single band,for example 800 to 900 MHz, portable radio transceiver in which theantenna comprises respective PIFA transmit and receive antennas formedas patches on a printed circuit board mounted above and facing areference ground plane of a circuit board on which the transmitter andreceiver components are mounted. Separate feeds interconnect an outputbandpass filter of the transmitter and an input bandpass filter of thereceiver with their respective patch antenna. An electrically conductivepedestal connects the reference ground plane to an elongate area of theprinted circuit extending between the patches. Both the transmit andreceive antennas are narrow band, say 1.6 MHz, antennas which aretunable over a wider bandwidth, say 25 MHz, by coupling reactivecomponents, that is capacitances or inductances, to the respectiveantennas using PIN diode switches.

Our pending unpublished PCT Patent Application IB02/05031 (Applicant'sreference PHGB 010194) discloses a wireless terminal having a dual bandPIFA comprising a substantially planar patch conductor. A first feedconductor comprises a first feed pin connected to the patch conductor ata first point, a second feed conductor comprises a second feed pinconnected to the patch conductor at a second point, and a groundconductor comprises a ground pin connected between a third point on thepatch conductor and a ground plane. The feed and ground pins may havedifferent cross-sectional areas to provide an impedance transformation.First and second transmission lines are formed by the ground conductorand a respective one of the feed conductors. The first and secondtransmission lines are short circuit transmission lines whose respectivelengths are defined by a first linking conductor connecting the firstfeed and ground pins and a second linking conductor connecting thesecond feed and ground pins. Complementary circuit elements comprisingfirst and second shunt capacitance means are coupled respectivelybetween the first and second feed pins and the ground pin. The describedantenna is fed by a diplexer to provide isolation between say GSMcircuitry operating over a frequency band 880 to 960 MHz and DCScircuitry operating over a frequency band of 1710 to 1880 MHz. Theprovision of a diplexer although enabling the cited antenna arrangementto work satisfactorily represents an undesired complication.

DISCLOSURE OF INVENTION

An object of the present invention is to simplify the architecture of awireless terminal.

According to a first aspect of the present invention there is provided awireless terminal having a dual band antenna arrangement comprising anantenna having a first feed for signals in a first, lower frequencyband, a second feed for signals in a second, higher frequency band and aground pin, first coupling means for coupling transmit and receive pathsof a first transceiver to the first feed, second coupling means forcoupling transmit and receive paths of a second transceiver to thesecond feed, each of the first and second coupling means comprising aquarter wavelength transmission line having a first end coupled to therespective transmit signal path and a second end coupled by bandpassfiltering means to the respective receive signal path, a first switchingdevice coupling a transmit signal path to the first end of therespective quarter wavelength transmission line, a second switchingdevice coupling the second end of the respective quarter wavelengthtransmission line to ground, and means for switching-on the first andsecond switching devices of one of the first and second coupling meanswhen in a transmit mode and for switching-off the first and secondswitching devices when in a is receive mode, the first and secondswitching devices of the other of the first and second coupling meansbeing non-conductive.

According to a second aspect of the present invention there is providedan RF module for use with a dual band antenna arrangement, the RF modulecomprising a first antenna feed for signals in a first, lower frequencyband, a second antenna feed for signals in a second, higher frequencyband and a ground pin, first coupling means for coupling transmit andreceive paths of a first transceiver to the first feed, second couplingmeans for coupling transmit and receive paths of a second transceiver tothe second feed, each of the first and second coupling means comprisinga quarter wavelength transmission line having a first end coupled to therespective transmit signal path and a second end coupled by bandpassfiltering means to the respective receive signal path, a first switchingdevice coupling a transmit signal path to the first end of therespective quarter wavelength transmission line, a second switchingdevice coupling the second end of the respective quarter wavelengthtransmission line to ground, and means for switching-on the first andsecond switching devices of one of the first and second coupling meanswhen in a transmit mode and for switching-off the first and secondswitching devices when in a receive mode, the first and second switchingdevices of the other of the first and second coupling means beingnon-conductive.

According to a third aspect of the present invention there is provided acombination of a RF module made in accordance with the second aspect ofthe present invention and an antenna having means for connection to thefirst and second feeds and the ground pin.

The antenna may comprise a patch antenna such as a PIFA (planarinverted-F antenna).

The ground pin may be disposed between, and insulated from, the firstand second feeds.

The first and second switching devices may comprise any suitable RFswitching devices such as PIN diodes.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example, with isreference to the accompanying drawings, wherein:

FIG. 1 is a block schematic diagram of an embodiment of a wirelessterminal made in accordance with the present invention,

FIG. 2 is a diagram of a circuit board having a PIFA and transmittingand receiving filters,

FIG. 3 is a Smith chart showing the performance of the terminal in theGSM transmit mode,

FIG. 4 is a graph showing the simulated return loss S₁₁ in dB againstfrequency in GHz for the GSM transmit mode,

FIG. 5 is a graph showing the total efficiency in the GSM transmit mode,

FIG. 6 is a graph showing the GSM transmit out-of-band attenuation,

FIG. 7 is a Smith chart showing the performance of the terminal in theDCS transmit mode,

FIG. 8 is a graph showing the simulated return loss S₁₁ in dB againstfrequency in GHz for the DCS transmit mode,

FIG. 9 is a graph showing the total efficiency in the DCS transmit mode,

FIG. 10 is a graph showing the DCS transmit out-of-band attenuation,

FIG. 11 is a Smith chart showing the performance of the terminal in theDCS receive mode,

FIG. 12 is a graph showing the simulated return loss S₁₁ in dB againstfrequency in GHz for the DCS receive mode,

FIG. 13 is a graph showing the total efficiency in the DCS receive mode,

FIG. 14 is a Smith chart showing the performance of the terminal in theGSM receive mode,

FIG. 15 is a graph showing the simulated return loss S₁₁ in dB againstfrequency in GHz for the GSM receive mode, and

FIG. 16 is a graph showing the total efficiency in the GSM receive mode.

In the drawings the same reference numerals have been used to indicatecorresponding features.

MODES FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, the wireless terminal comprises a PIFA antenna 10having feeds 12 and 14 to which are connected a GSM transceiver whichoperates in a frequency band of 880 to 960 MHz and a DCS transceiverwhich operates in the frequency band 1710 to 1880 MHz, respectively. Aground pin 16 is provided between the feeds 12, 14 as shown in FIG. 2 tobe described later. As the architectures of the GSM and the DCStransceivers are generally the same the corresponding stages will bereferenced with the suffices A and B respectively and in the interestsof brevity only the GSM transceiver will be described. The transmittersection of the GSM transceiver comprises a signal input terminal 18Acoupled to an input signal processing stage 20A. The stage 20A iscoupled to a modulator 22A which provides a modulated signal to atransmitter stage 24A which includes a frequency up-converter, poweramplifier and any relevant filters. A common coupling stage 26A couplesthe transmitter stage to the antenna feed 12. The common coupling stages26A and 26B will be described in greater detail later. The couplingstage 26A is also coupled to a receiver section 28A of the GSMtransceiver to the feed 10. The receiver section 28A includes a lownoise amplifier, a frequency down-converter and filters. An output ofthe receiver section 28A is demodulated in a demodulator 30A and itsoutput is applied to a signal processing stage 32A which provides anoutput signal on a terminal 34A. The operation of both of thetransceivers is controlled by a processor 36.

Referring to FIG. 2, a printed circuit board PCB has components (notshown) on one side and a ground plane GP on the reverse side. A PIFA 10is mounted on, or carried by, the PCB. The PIFA can be implemented inseveral alternative ways, for example as a preformed metal plate carriedby the PCB using posts of an insulating material, as a pre-etched pieceof printed circuit board carried by the PCB, as a block of insulatingmaterial having the PIFA formed by selectively etching a conductivelayer provided on the insulating material or by selectively printing aconductive layer on the insulating block or as an antenna on the cellphone case. For use at GSM and DCS frequencies, the dimensions of thePIFA 10 are length (dimension “a”) 40 mm, height (dimension “b”) 8 mmand depth (dimension “c”) 4 mm. The planar conductor or conductive layerincorporates a slot 40 comprising four interconnected rectilinearsections 40A to 40D having an overall shape approximating to an invertedquestion mark without the dot. The section 40A which opens into the topedge of the PIFA 10 is wider than the sections 40B to 40D which havesubstantially the same width. The slot 40 can be considered as dividingthe planar conductor into two antennas connected to a common feed,namely a smaller central radiator R1 for the DCS frequency band and alonger radiator R2, wrapped around the central radiator R1, for the GSMfrequency band.

The feeds 12, 14 are on either side of the ground pin 16 and the spacesbetween the feed and ground pins 12, 14, 16 have been partially filledwith a conductive material 42 to leave unfilled gaps G1 and G2, each ofthe order of 2 mm. The sizes of the gaps could be different on eitherside of the ground pin 16 in order to optimise independently each band.It can be seen that the feed pin 12 for GSM is wider than the feed pin14 in order that the common mode impedance transformation is differentfor both bands.

Other arrangements of the feed pins 12, 14 and the ground pin 16 to thatshown in FIG. 2 are possible. For example the ground pin 16 could beoffset to one side of the feed pins 12,14.

Due to the conductive material 42 partially filling the spaces betweenthe respective feed pins 12, 14 and the ground pin 16, the PIFAincorporates a low valued shunt inductance across each feed. Thisinductance is tuned by shunt capacitors 46A, 46B (FIG. 1) on each feedby resonating with it at the resonant frequency of the antenna. Sincethe feeds are independent, each capacitance can be independentlyoptimised, resulting in more wide band performance for both bands withno compromise required between the two bands. In order to prevent energyfrom being transferred between the two feeds 12, 14, the antenna isco-designed with the RF front end by the provision of the commoncoupling stages 26A, 26B.

Reverting to the coupling stages 26A, 26B shown in FIG. 1, apart fromone difference in the stage 26B, the architectures of these stages isthe same although the component values are selected for the particularfrequencies of use and where appropriate the same reference numeralswith the suffix A or B have been used to indicate correspondingcomponents in the coupling stages 26A and 26B, respectively.

For convenience the coupling stage 26A will be described and thereference numerals of the corresponding components in the coupling stage26B will be shown in parentheses. The output of the transmitting stage24A (24B) is coupled to the anode of a low loss PIN diode D1 (D3), thecathode of which is coupled to one end of a series inductance 48A (48B).The other end of the inductance 48A (48B) is coupled to the feed 12(14), to the shunt capacitor 46A (46B) and to one end of a quarterwavelength (λ/4) transmission line 50A (50B). The other end of thetransmission line 50A (50B) is coupled to the anode of a low loss PINdiode D2 (D4), the cathode of which is coupled to ground, and to aninput of a band pass filter 52A (52B). The filters 52A, 52B may compriseSAW filters. The output of the filter 52A (52B) is coupled to the inputof the receiver section 28A (28B).

If the filter 52B is implemented as a SAW filter, a RF resonant trapcircuit 54 is provided in the signal path from the other end of thetransmission line 50B to the input of the band pass filter 52B. The trapcircuit comprises a series capacitor 56 and a shunt inductance 58 whichis coupled to ground by way of a capacitor 60. The value of thecapacitor 60 is selected to tune the inductance 58 so that the voltageat the input to the filter 52B is reduced. Typically such SAW filterscan handle in-band signals of up to a power of 13 dBm. However forout-of-band signals a higher power can be delivered to such a filterwhich is useful as a GSM signal can have a power of up to 30 dBm. In analternative implementation BAW (Bulk Acoustic Wave) filters may beconsidered as they exhibit the same out-of-band impedancecharacteristics to resonant SAW devices and also they do not suffer fromthe power handling restrictions which apply to SAW filters.

The switching of the PIN diodes D1 to D4 is controlled by the processor36 in accordance with the following truth table.

D1 D2 D3 D4 GSM Tx On On Off Off GSM Rx Off Off Off Off DCS Tx Off OffOn On DCS Rx Off Off Off Off

In operation when the GSM transmitter is operating and the DCStransmitter is inactive, the PIN diodes D1, D2 are conductive so thatthe signal is applied to the feed 12. The other end of the transmissionline is open circuit with the result that the transmitted signal doesnot enter the receiver section 28A. A similar situation occurs when theDCS transmitter is operating and the PIN diodes D3, D4 are conductive.

When a GSM signal is being received the PIN diodes D1, D2 arenon-conductive, as are the PIN diodes D3, D4. The received signal passesthrough the transmission line 50A and is passed by the band pass filter52A to the receiver section 28A. By the feeds 12 and 14 being on theopposite sides of the ground pin 16, the band pass filter 52B appearsreflective to the GSM signal thereby attenuating or blocking thissignal. Any GSM signal which is present at the input to the band passfilter 52B will in any event be blocked by the filter. The converse istrue when a DCS signal is being received by the receiver section 28B.

The dual feed allows independent optimisation and broad band operationin both the GSM and DCS bands. The integrated design of the antenna,matching circuitry and filtering allows a better overall match andefficiency with a simple architecture.

In assessing the performance of the PIFA and the associated couplingstages 26A, 26B, the following assumptions/simplifications have beenmade. The PIN diodes are represented by 2 Ω series resistors in the “On”state and 0.25 pF series capacitors in the “Off” state. The antennaefficiency is not included-all power in the antenna is assumed to beradiated. Ideal transmission lines 50A, 50B have been used. Allcomponents are assigned Q's of 50 (constant with frequency). This isregarded as being slightly optimistic for inductors and pessimistic forcapacitors (dependent on technology, frequency and so forth).

The performance of the circuit shown in FIG. 1 when operating in the GSMtransmit mode is illustrated by in FIG. 3 by a Smith chart and in FIG. 4by a graph showing the simulated return loss S₁₁ in dB against frequencyF in GHz. In FIGS. 3 and 4 the arrows GTX1 and GTX2 refer respectivelyto a frequency/attenuation of 880 MHz/−20.205 dB and 915 MHz/−9.513 dB.Here the antenna is slightly mismatched in order to achieve balancededge efficiencies as shown in FIG. 5 in which the arrow e1 indicates afrequency of 915 MHz and a total efficiency of 0.710 and the arrow e2indicates a frequency of 880 MHz and a total efficiency of 0.659. Therelatively low efficiency (65%) at 880 MHz is due largely to the Q ofthe capacitor 46A (FIG. 1) at the GSM input to the antenna. It is feltthat this can be improved by using a better quality component and bybetter optimisation of the antenna impedance. FIG. 6 illustrates thecorresponding out-of-band attenuation (mostly provided by the antenna).The arrows G1, G2, G3 and G4 respectively represent thefrequency/efficiencies of 880 MHz/−1.812 dB, 915 MHz/−1.490 dB, 1.785GHz/−33.627 dB and 2.640 GHz/−42.184 dB. The combination of the antennaand the circuitry provides high levels of second (−33 dB) and third (−42db) harmonic suppression.

In the DCS transmit mode the PIN diodes D1 and D2 are both “Off” whilethe PIN diodes D3 and D4 are “On”. In this condition the GSM transmitteris isolated predominantly by the PIN diode D1. The GSM receiver SAWfilter 52A is isolated predominantly by the antenna 10 being reflective.At the input of the GSM receiver SAW filter 52A the worst case isolationis approximately −26 dB, giving a power of 4 dBm. This is significantlyless than the power rating of the SAW filter. The voltage developed isapproximately 0.7V which is less than would occur in-band at the maximumpower rating. Thus, in the GSM branch a resonant trap is not required.

The performance of the circuit shown in FIG. 1 when operating in the DCStransmit mode is illustrated in FIG. 7 by a Smith chart and in FIG. 8 bya graph showing the simulated return loss S₁₁ in dB against frequency Fin GHz. In FIGS. 7 and 8 the arrows DTX1 and DTX2 refer respectively toa frequency/attenuation of 1.710 GHz/−9.532 dB and 1.785 GHz/−13.782 dB.FIG. 9 illustrates optimising the simulated return loss S₁₁ forefficiency. In FIG. 9 the arrow e1 indicates a frequency of 1.795 GHzand a total efficiency of 0.823 and the arrow e2 indicates a frequencyof 1.710 GHz and a total efficiency of 0.752. The correspondingout-of-band attenuation (mostly provided by the antenna) is shown inFIG. 10. The arrows G1, G2, G3 and G4 respectively represent thefrequency/efficiencies of 1.710 GHz/−1.236 dB, 1.795 GHz/−0.844 dB,3.000 GHz/−24.540 dB and 3.000 GHz/−24.540 dB. It is anticipated thatthis configuration will provide reasonable levels of second or thirdharmonic suppression.

In the DCS receive mode all the PIN diodes are “Off”. The performance ofthe circuit shown in FIG. 1 when operating in the DCS receive mode isillustrated in FIG. 11 by a Smith chart and in FIG. 12 by a graphillustrating the simulated return loss S₁₁ in dB against frequency F inGHz. In FIGS. 11 and 12 the arrows DRX1 and DRX2 refer respectively to afrequency/attenuation of 1.805 GHz/−12.743 dB and 1.880 GHz/−7.503 dB.The DCS receive mode efficiency is shown in FIG. 13. In FIG. 13 thearrow e1 indicates a frequency of 1.805 GHz and a total efficiency of0.405 and the arrow e2 indicates a frequency of 1.880 GHz and a totalefficiency of 0.414. The worst case band edge loss in this mode isnearly 4 dB. This is approximately 2 dB higher than for a filter in a 50Ω system. The additional loss is primarily due to impedance mismatchpresented by the antenna and seems sensitive to the impedance (forexample, whether the antenna presents an inductive or capacitive load).In a conventional antenna system this mechanism is expected to givesignificantly more additional loss.

The performance of the circuit shown in FIG. 1 when operating in the GSMreceive mode is illustrated in FIG. 14 by a Smith chart and in FIG. 15by a graph illustrating the simulated return loss S₁₁ in dB againstfrequency F in GHz. In FIGS. 14 and 15 the arrows referenced GRX1 andGRX2 refer respectively to frequencies/attenuations of 925 MHz/−11.298and 960 MHz/−11.578. FIG. 16 shows the GSM receive mode efficiency, thearrow e1 indicates a frequency of 925 MHz and a total efficiency of0.496 and the arrow e2 indicates a frequency of 960 MHz and a totalefficiency if 0.478.

The performance of the circuit illustrated in FIG. 1 is regarded asbeing superior to the of a conventional configuration using a diplexerin the following areas:

-   -   (1) The total efficiency (including the effects of antenna        mismatch) is greater.    -   (2) The match at the power amplifiers and low noise amplifiers        is improved.    -   (3) The antenna and associated circuitry provide a high degree        of harmonic filtering. the filtering requirements of the rest of        the module can be reduced if this is taken into consideration.

Points (1) and (2) are regarded as being particularly important. If anRF module is designed without consideration of the antenna, the inputmatch and efficiency will be poor when connected to a typical antenna.Since the RF is contained within the module, there is no opportunity tocounter the effects of the antenna at intermediate circuit stages.

Although the present invention has been described with reference to awireless terminal having a PIFA antenna and operating in the GSM and DCSbands. The invention may be applied to any multiband radio and in otherdual band applications. Also the present invention relates to an RFmodule having an antenna and at least those components included in thecoupling stages 26A and 26B.

In the present specification and claims the word “a” or “an” precedingan element does not exclude the presence of a plurality of suchelements. Further, the word “comprising” does not exclude the presenceof other elements or steps than those listed.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in the design, manufacture anduse of wireless terminals and component parts therefor and which may beused instead of or in addition to features already described herein.

INDUSTRIAL APPLICABILITY

Multiband Wireless terminals, for example dual band mobile telephones.

1. A wireless terminal having a dual band antenna arrangement comprisingan antenna (10) having a first feed (12) for signals in a first, lowerfrequency band, a second feed (14) for signals in a second, higherfrequency band and a ground pin (16), first coupling means (26A) forcoupling transmit and receive paths of a first transceiver to the firstfeed, second coupling means (26B) for coupling transmit and receivepaths of a second transceiver to the second feed, each of the first andsecond coupling means comprising a quarter wavelength transmission line(50A, 50B) having a first end coupled to the respective transmit signalpath and a second end coupled by bandpass filtering means (52A, 52B) tothe respective receive signal path, a first switching device (D1, D3)coupling a transmit signal path to the first end of the respectivequarter wavelength transmission line, a second switching device (D2, D4)coupling the second end of the respective quarter wavelengthtransmission line to ground, and means (36) for switching-on the firstand second switching devices of one of the first and second couplingmeans when in a transmit mode and for switching-off the first and secondswitching devices when in a receive mode, the first and second switchingdevices of the other of the first and second coupling means beingnon-conductive.
 2. A wireless terminal as claimed in claim 1,characterised in that the antenna is a planar inverted-F antenna.
 3. Awireless terminal as claimed in claim 1 or 2, characterised in that theground pin (16) is disposed between, and insulated from, the first (12)and second (14) feeds.
 4. A wireless terminal as claimed in claim 1, 2or 3, characterised by means (56, 58, 60) for reducing the voltage at asignal input of the band pass filtering means of the second couplingmeans.
 5. A wireless terminal as claimed in any one of claims 1 to 4,characterised in that the first and second switching devices comprisePIN diodes.
 6. An RF module for use with a dual band antennaarrangement, the RF module comprising a first antenna feed (12) forsignals in a first, lower frequency band, a second antenna feed (14) forsignals in a second, higher frequency band and a ground pin (16), firstcoupling means (26A) for coupling transmit and receive paths of a firsttransceiver to the first feed, second coupling means (26B) for couplingtransmit and receive paths of a second transceiver to the second feed,each of the first and second coupling means comprising a quarterwavelength transmission line (50A, 50B) having a first end coupled tothe respective transmit signal path and a second end coupled by bandpass filtering means (52A, 52B) to the respective receive signal path, afirst switching device (D1, D3) coupling a transmit signal path to thefirst end of the respective quarter wavelength transmission line, asecond switching device (D2, D4) coupling the second end of therespective quarter wavelength transmission line to ground, and means(36) for switching-on the first and second switching devices of one ofthe first and second coupling means when in a transmit mode and forswitching-off the first and second switching devices when in a receivemode, the first and second switching devices of the other of the firstand second coupling means being non-conductive.
 7. A RF module asclaimed in claim 6, characterised in that the ground pin (16) isdisposed between, and insulated from, the first (12) and second (14)feeds.
 8. A RF module as claimed in claim 6 or 7, characterised by means(56, 58, 60) for reducing the voltage at a signal input of the band passfiltering means of the second coupling means.
 9. The combination of a RFmodule as claimed in claim 6, 7 or 8, and an antenna (10) having meansfor connection to the first and second feeds (12, 14) and the ground pin(16).
 10. The combination as claimed in claim 9, characterised in thatthe antenna is a planar inverted-F antenna.